1. Field of the Invention
This invention relates to a computer system of a single-instruction-multiple-data (SIMD) type having a plurality of processing elements, more particularly to its optical processing element topology.
2. Discussion of the Prior Art
A single-instruction-multiple-data (SIMD) machine is a computer system that consists of a control unit, N processing elements (PEs) and an interconnect network. Each processing element has its own local memory and registers, and simultaneously executes an identical instruction. The interconnect network provides a communication link for the processing elements. The control unit provides or broadcasts control and communication commands to the processing elements.
The SIMD machine is of particular interest in arithmetic computations, such as matrix-vector processing, digital Fourier transformation, data sorting, as well as in various image processing applications. However, since the SIMD processing environment requires an identical processing or interconnect to be performed at each time cycle, for a machine having a large number (large N) of processing elements and a fast clock rate, interconnect latency results in processing bottlenecks.
To solve this problem, various optical guided-wave and free-space interconnect architectures have been proposed. A common feature of these types of interconnects is that the processing data and/or the processing elements are distributed as a rectangular array. This rectangular array topology has lead; and to successful implementations of some types of networks such as the Optical Perfect Shuffle network and the Cross-over Interconnect network. However, the optical implementation of other important types of interconnect networks, such as the Nearest-neighbor Interconnect (NNI), the Barrel-shifter Interconnect (also known as the plus-minus 2.sup.i (PM2I) Interconnect), the Chordal Ring Interconnect (CRI), and the Hyper-Cube Interconnect (HCI) networks, has not been successful.
The rectangular array topology has a major problem in that its optical implementation requires the use of both shift-in-variant and shift-variant optical elements in the network. For example, the NNI and PM2I networks require linear space invariant operations for their center processing elements and space variant (or wraparound) operations for their edge and corner processing elements. The use of state-of-the-art multifaceted computer-generated-holograms has been proposed to solve the problem. However, even with the use of the holograms, the rectangular array topology still has interconnect latency (or clock-skew) problems in that signals transmitted through different space-invariant and space-variant elements in the interconnect network undergo different delays, thus seriously limiting the processing rate of the SIMD machine.